Grain-oriented electrical steel sheet and method for manufacturing the same

ABSTRACT

The grain-oriented electrical steel sheet according to one embodiment of the present invention includes, by weight, Si: 1.0 to 7.0%, B: 0.001 to 0.1%, and Ba and Y individually or in a total amount of 0.005 to 0.5%, and the remainder includes Fe and other unavoidable impurities.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed to a grain-oriented electrical steelsheet and a method of manufacturing the same. More specifically, thepresent invention relates to a grain-oriented electrical steel sheetcontaining B, Ba, and Y in a predetermined amount to be segregated ingrain boundaries, and a method for manufacturing the same.

BACKGROUND OF THE INVENTION

The grain-oriented electrical steel sheet is a soft magnetic materialhaving excellent magnetic properties in the rolling direction, composedof grains having a crystal orientation of {110}<001>, so-called Gossorientation. In general, magnetic properties can be expressed bymagnetic flux density and iron loss, and high magnetic flux density canbe obtained by precisely aligning the orientation of the grains to the{110}<001> orientation. The electrical steel sheet having a highmagnetic flux density not only makes it possible to reduce the size ofthe iron core material of the electric equipment, but also reduces thehysteresis loss, thereby making it possible to miniaturize the electricequipment and increase the efficiency at the same time. The iron loss isa power loss consumed as heat energy when an arbitrary alternatingmagnetic field is applied to the steel sheet, and varies greatlydepending on the magnetic flux density and plate thickness of the steelsheet, the amount of impurities in the steel sheet, the specificresistance and the size of the secondary recrystallization grain. Thehigher the magnetic flux density and the specific resistance and thelower the plate thickness and the amount of impurities in the steelsheet, the lower the iron loss, thereby increasing the efficiency of theelectrical equipment.

In order to cope with global warming by reducing CO2 emission worldwide,there is a tendency toward energy saving and high-efficiencycommercialization. Further, as the demand for widening and spreading ofhighly efficient electric devices using less electric energy isincreased, the social demand for the development of a grain-orientedelectrical steel sheet having a low iron loss property is increasing.

Generally, a grain-oriented electrical steel sheet having excellentmagnetic properties is required to strongly develop a Goss texture in a{110} <001> orientation in the rolling direction of a steel sheet. Inorder to form such a texture, grains in the Goss orientation should forman abnormal grain growth called the second recrystallization. Thisabnormal grain growth occurs when normal grain growth inhibits themovement of grain boundaries normally grown by precipitates, inclusions,or elements dissolved or segregated in the grain boundaries, unlikeordinary grain growth. As described in the above, precipitates andinclusions that inhibit grain growth are specifically referred to as agrain growth inhibitor. Studies on the production of grain-orientedelectrical steel sheets by secondary recrystallization in the {110}<001>orientation has been focused on securing good magnetic properties byusing a grain growth inhibitor to form secondary recrystallization withhigh degree of integration in the {110} <001> orientation.

In the conventional grain-oriented electrical steel sheet technology,precipitates such as AlN and MnS[Se] are mainly used as a grain growthinhibitor. For example, decarburization is carried out after one time ofthe strong cold-rolling. And then nitrogen is supplied to the inside ofthe steel sheet through a separate nitriding process using ammonia gasto produce secondary recrystallization by the Al-based nitride whichexhibits a strong grain growth inhibiting effect.

However, in the process of high temperature annealing, the instabilityof the precipitates due to the denitrification or the re-nitrificationbased on the furnace atmosphere and the necessity of the stress reliefannealing for a long time for 30 hours or more at a high temperaturecauses the complications and cost burden.

For this reason, recently, a method of manufacturing a grain-orientedelectrical steel sheet without using a precipitates such as AlN or MnSas a grain growth inhibitor has been proposed. For example, there is amanufacturing method using grain boundary segregation elements such asbarium (Ba) and yttrium (Y).

Ba and Y are excellent in the effect of inhibiting the growth of grainsenough to form secondary recrystallization and are not affected by theatmosphere in the furnace during the high-temperature annealing process.However, they have a disadvantage in weakening the bonding strength ofthe grain boundaries. Therefore, there is a problem in that a largenumber of grain boundary cracks occur in the cold-rolling process inwhich the high pressure is required, so that the productivity decreasecannot be avoided.

DETAILS OF THE INVENTION Problems to be Solved

In one embodiment of the present invention, a grain-oriented electricalsteel sheet and a method of manufacturing the same are provided.

Means to Solve the Problems

The grain-oriented electrical steel sheet according to one embodiment ofthe present invention may include, by weight, Si: 1.0 to 7.0%, B: 0.001to 0.1%, and Ba and Y individually or in a total amount of 0.005 to0.5%, and the remainder including Fe and other unavoidable impurities.

The grain-oriented electrical steel sheet according to one embodiment ofthe present invention may satisfy the following Formula (1).

0.5≤([Ba]+[Y])/([B]*10)≤3   [Formula 1]

(In the Formula (1), [Ba], [Y], and [B] represent the contents (% byweight) of Ba, Y and B, respectively.)

The grain-oriented electrical steel sheet according to one embodiment ofthe present invention may further include C: 0.005% or less (excluding0%), Al: 0.005% or less (excluding 0%), N: 0.0055% or less (excluding0%), and S: 0.0055% or less.

The grain-oriented electrical steel sheet according to one embodiment ofthe present invention may further include Mn: 0.01% to 0.5%. The averageparticle diameter of the grains may have a particle diameter of 2 mm ormore is 10 mm or more.

The grain-oriented electrical steel sheet according to one embodiment ofthe present invention may include B and, Ba or Y segregated in grainboundaries.

The method for manufacturing a grain-oriented electrical steel sheetaccording to an embodiment of the present invention may include a stepof heating the slab including, by weight, Si: 1.0 to 7.0%, B: 0.001 to0.1%, and Ba and Y individually or in a total amount of 0.005 to 0.5%,and the remainder including Fe and other unavoidable impurities; a stepof hot-rolling the slab to produce a hot-rolled sheet; a step ofcold-rolling the hot-rolled sheet to produce a cold-rolled sheet; a stepof the primary recrystallization annealing the cold-rolled sheet; and astep of the second recrystallization annealing the cold-rolled sheetafter the primary recrystallization annealing is completed.

The slab may satisfy the following formula (1).

0.5≤([Ba][Y])/([B]*10)≤3   [Formula 1]

(In the formula (1), [Ba], [Y], and [B] represent the contents (% byweight) of Ba, Y, and B, respectively.)

The slab may further include C: 0.001 to 0.1%, Al: 0.01% or less(excluding 0%), N: 0.0055% or less (excluding 0%) and S: 0.0055% or less(excluding 0%).

The slab may further include Mn: 0.01% to 0.5%.

In the step of heating the slab, it can be heated to 1000 to 1280° C.

In the step of cold-rolling the hot-rolled sheet to produce acold-rolled sheet, the final reduction roll may be 80% or more.

the second recrystallization annealing step may include a temperatureelevating step and a cracking step, and the temperature of the crackingstep is 900 to 1250° C.

Effects of the Invention

The grain-oriented electrical steel sheet according to an embodiment ofthe present invention is excellent in magnetic properties by stablyforming

Goss Grain.

In addition, since AIN and MnS are not used as a grain growth inhibitor,it is not necessary to heat the slab at a high temperature of 1300° C.or more. In addition, due to the grain boundary strengthening effect,generation of grain boundary cracks is reduced even under a strongcold-rolling. Thus, the productivity is increased and manufacturing costis reduced.

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FIG. 1 is a photograph of a cold-rolled steel sheet in the process ofmanufacturing the inventive material, which is a sample No. 2.

FIG. 2 is a photograph of a cold-rolled steel sheet in the process ofmanufacturing the comparative material, which is a sample No. 1.

DETAILED DESCRIPTIONS OF THE INVENTION

The terms first, second, third, and the like are used to describevarious portions, components, regions, layers and/or sections, but arenot limited thereto. These terms are only used to distinguish oneportion, component, region, layer or section from another portion,component, region, layer or section. Thus, a first portion, component,region, layer or section described below may be referred to as a secondportion, component, region, layer or section without departing from thescope of the present invention. The terminology used herein is for thepurpose of describing particular embodiments only and is not intended tolimit the invention. The singular forms as used herein include pluralforms as long as the phrases do not specifically state the oppositemeaning thereof. The “comprises” means that a particular characteristic,region, integer, step, motion, element and/or component is specified andthat does not exclude the presence or addition of other characteristics,regions, integers, steps, motions, elements, and/or components.

When referring to a part as being “on” or “above” another part, it maybe positioned directly on or above another part, or another part may beinterposed therebetween. In contrast, when referring to a part being“directly above” another part, no other part is interposed therebetween.Unless defined otherwise, all terms including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which the present invention belongs. Termsdefined in the commonly used dictionary are further interpreted ashaving a meaning consistent with the relevant technical literature andthe present disclosure, and are not to be construed as ideal or veryformal meanings unless defined otherwise.

Unless otherwise stated, % means % by weight, and 1 ppm is 0.0001% byweight.

Hereinafter, embodiments of the present invention will be described indetail so that a person of ordinary skill in the art could easily carryout the present invention. The present invention may, however, beembodied in various forms and should not be construed as limited to theembodiments set forth herein.

In the conventional grain-oriented electrical steel sheet technology,precipitates such as AIN and MnS were used as the grain growthinhibitors. All the processes were strictly controlling the distributionof the precipitates and the process conditions were severely constrainedby the conditions for removing precipitates remaining in the secondaryrecrystallized steel sheet. On the other hand, in one embodiment of thepresent invention, precipitates such as AlN and MnS are not used as agrain growth inhibitor. In one embodiment of the present invention, byusing B and Ba or Y as a grain growth inhibitor, it is possible toincrease the grain fraction of Goss and obtain an electrical steel sheetexcellent in magnetic properties.

The grain-oriented electrical steel sheet according to one embodiment ofthe present invention may include, by weight, Si: 1.0 to 7.0%, Mn: 0.01to 0.5%, B: 0.001 to 0.1%, and Ba and Y individually or in a totalamount of 0.005 to 0.5%, and the remainder including Fe and otherunavoidable impurities.

Hereinafter, each component will be described in detail.

In one embodiment of the present invention, barium (Ba) and yttrium (Y)act as a grain growth inhibitor, during secondary recrystallizationannealing, to suppress the growth of grains in a orientation other thanthe Goss grains, thereby improving the magnetic properties of theelectrical steel sheet. Ba and Y may be added individually or incombination. Ba and Y may be included individually or in a total amountof 0.005 to 0.5% by weight. That is, when Ba or Y is added individually,the content of Ba or Y may be 0.005 wt % to 0.5 wt %, respectively. WhenBa and Y are simultaneously added, the sum of the contents (i.e., thetotal amount) of Ba and Y may be 0.005 wt % to 0.5 wt %. If the amountof Ba or Y or the total amount thereof is too small, it is difficult toexert a sufficient restraining force. If the amount of Ba or Y or thetotal amount thereof is too large, the brittleness of the steel sheetincreases and cracks may occur during rolling. Boron (B) is segregatedat the grain boundaries to strengthen the grain boundary bonding force,thereby reducing generation of cracks and rolling times during rolling.In addition, it reacts with nitrogen in the steel to partially form BNprecipitates. BN is excellent in high temperature stability and can actas an auxiliary inhibitor which suppresses grain growth together with Baand Y described in the above. The content of B may be 0.001 to 0.1% byweight. If B is included too little, it may be insufficient to alleviatethe grain boundary brittleness due to Ba and Y. If B is included toomuch, grain boundary segregation of Ba and Y is suppressed, and a largenumber of inclusions are formed in the high-temperature annealingprocess, so that the magnetic properties may be deteriorated. B maysatisfy the following Formula 1 in relation to Ba and Y.

0.5≤([Ba]+[Y])/([B]*10)≤3   [Formula 1]

(In the formula (1), [Ba], [Y] and [B] represent the contents (% byweight) of Ba, Y and B, respectively.)

When the value of the Formula 1 is less than 0.5, grain boundarysegregation of Ba and Y is suppressed. Further, a large number ofinclusions are formed in the high-temperature annealing process, so thatthe magnetic properties may be deteriorated. When the value of theFormula 1 is more than 3, it may be insufficient to alleviate the grainboundary brittleness due to Ba and Y.

Silicon (Si) acts to lower the iron loss by increasing the specificresistance of the material. If the Si content in the slab and theelectrical steel sheet is less than 1.0% by weight, the specificresistance may decrease and the iron loss property may be deteriorated.On the contrary, when the Si content exceeds 7% by weight in thegrain-oriented electrical steel sheet, the Si content in thegrain-oriented electrical steel sheet can be 7% by weight or less sincethe processing is difficult in manufacturing the transformer. Carbon(C), as an austenite stabilizing element, is added to the slab in anamount of 0.001 wt% or more to refine the coarse columnar structure thatoccurs during the performance process and to suppress the slab centersegregation of S. It is also possible to accelerate work hardening ofthe steel sheet during cold-rolling, thereby promoting generation ofsecondary recrystallization nuclei in the {110} <001> orientation in thesteel sheet. However, if the content exceeds 0.1%, it may causeedge-cracks in hot-rolled steel. However, the decarburization annealingis performed during the production of the electrical steel sheet, andthe C content in the final electrical steel sheet after decarburizationannealing may be 0.005 wt % or less. More specifically, it may be 0.003%by weight or less.

In one embodiment of the present invention, the precipitates, such asAlN and MnS, are not used as a grain growth inhibitor. Therefore, theelements which are essentially used in normal grain-oriented electricalsteel sheets, such as aluminum (Al), nitrogen (N), sulfur (S), areregulated within the range of impurities. That is, when Al, N, and S areinevitably further included, it may further include 0.005 wt % or lessof Al, 0.0055 wt % or less of S, and 0.0055 wt % or less of N.

In one embodiment of the present invention, since AlN is not used as agrain growth inhibitor, aluminum (Al) content can be positivelysuppressed. Therefore, in one embodiment of the present invention, Almay not be added to the grain-oriented electrical steel sheet or may becontrolled to 0.005 wt % or less. In addition, in the slab, since Al canbe removed during the manufacturing process, Al can be contained in anamount of 0.01 wt % or less.

Since nitrogen (N) forms precipitates such as AN, (Al,Mn)N, (Al,Si,Mn)N, Si₃N₄, and BN, in the embodiment of the present invention, Nmay not be added or may be controlled to 0.0055 wt % or less. Morespecifically, it may be 0.0030% by weight or less. In one embodiment ofthe present invention, the nitriding process can be omitted, so that theN content in the slab and the N content in the final electrical steelsheet can be substantially the same.

The sulfur (S) is an element having a high dissolving temperature and ahigh segregation during hot-rolling, and thus, in one embodiment of thepresent invention, it may not be added or may be controlled to 0.0055 wt% or less. More specifically, it may be 0.0035% by weight or less.

In one embodiment of the present invention, since MnS is not used as agrain growth inhibitor, manganese (Mn) may not be added. However, sinceMn is a non-resistive element and has an effect of improving magneticproperties, it may be further included as an optional component in slabsand electrical steel sheets. When Mn is further included, the content ofMn may be 0.01 wt % or more. However, if it exceeds 0.5% by weight,phase transformation may occur after the secondary recrystallization,and the magnetic property may be deteriorated. In the embodiment of thepresent invention, when additional elements are further included, it isunderstood that it is added replacing iron (Fe) which is the remainder.

In addition, as other unavoidable impurities, components such as Ti, Mg,and Ca react with oxygen in the steel to form oxides, which mayinterfere with the magnetic migration of the final product as aninclusion and cause magnetic deterioration. Thus, it is necessary tostrongly suppress the unavoidable impurities. Therefore, when they areinevitably contained, they can be controlled to 0.005% by weight or lessfor each component.

The grain-oriented electrical steel sheet according to an embodiment ofthe present invention has 10 mm or more of an average particle diameterof grains having 2 mm or more of the particle diameter. If the averageparticle diameter of the grains having a particle diameter of 2 mm ormore is less than 10 mm, the grains may not grow sufficiently and thusthe magnetic properties may be deteriorated. In one embodiment of thepresent invention, the particle diameter of grains means the diameterlength of the grains of the circular form.

The grain-oriented electrical steel sheet according to an embodiment ofthe present invention is excellent in magnetic properties by stablyforming Goss grain. Specifically, the grain-oriented electrical steelsheet according to an embodiment of the present invention may have amagnetic flux density Bs of 1.88 T or more measured at a magnetic fieldof 800 A/m.

The method for manufacturing a grain-oriented electrical steel sheetaccording to an embodiment of the present invention may include a stepof heating the slab containing, by weight, Si: 1.0 to 7.0%, B: 0.001 to0.1%, and Ba and Y individually or in a total amount of 0.005 to 0.5%,and the remainder including Fe and other unavoidable impurities; a stepof hot-rolling the slab to produce a hot-rolled sheet; a step ofcold-rolling the hot-rolled sheet to produce a cold-rolled sheet; a stepof the primary recrystallization annealing the cold-rolled sheet; and astep of the second recrystallization annealing the cold-rolled sheetafter the primary recrystallization annealing is completed.

Hereinafter, a manufacturing method of the grain-oriented electricalsteel sheet will be described in detail for each step.

First, the slab is heated.

Since the composition of the slab has been described in detail withrespect to the composition of the electrical steel sheet, a duplicateexplanation will be omitted.

The heating temperature of the slab is not limited. However, if the slabis heated to a temperature of 1280° C. or less, it may prevent thecolumnar structure of the slab from becoming coarse, thereby preventingcracks in the plate during the hot-rolling process. Thus, the heatingtemperature of the slab may be between 1000° C. and 1280° C. Inparticular, in one embodiment of the present invention, since AlN andMnS are not used as a grain growth inhibitor, it is not necessary toheat the slab at a high temperature of 1300° C. or more.

Next, the slab is hot-rolled to produce a hot-rolled sheet. Thehot-rolling temperature is not limited, and in one embodiment,hot-rolling may be terminated at 950° C. or lower. Thereafter, it iswater-cooled and can be wound at 600° C. or less.

Next, the hot-rolled sheet can be subject to a hot-rolled sheetannealing, if necessary. In the case of annealing the hot-rolled sheet,the hot-rolled steel sheet can be heated to a temperature of 900° C. ormore, cracked, and cooled to make the texture of the hot-rolled steelsheet uniform. Next, the hot-rolled sheet is cold-rolled to produce acold-rolled sheet. The cold-rolling can be carried out by a cold-rollingmethod using a reverse rolling mill or a tandem rolling mill through onecold-rolling, a plurality of cold-rolling, a plurality of cold-rollingincluding an intermediate annealing to produce a cold-rolled sheethaving a thickness of 0.1 mm to 0.5 mm.

Further, warm-rolling in which the temperature of the steel sheet ismaintained at 100° C. or higher during the cold-rolling can beperformed. In addition, the final reduction roll through cold-rollingcan be 80% or more. In an embodiment of the present invention, asdescribed in the above, by containing a specific amount of B in the slabcomponent, the grain boundary is segregated to strengthen the grainboundary's bonding force. As a result, cracking and rolling times can bereduced during rolling and the final reduction roll can be increased.

Next, the cold-rolled sheet is subject to the primary recrystallizationannealing. The primary recrystallization occurs in which the core of theGoss grain nuclei is generated in the primary recrystallizationannealing step. The decarburization of the cold-rolled sheet can beperformed in the primary recrystallization annealing step. It can beannealed at a temperature of 800° C. to 900° C. for decarburization.Further, the atmosphere may be a mixed gas atmosphere of hydrogen andnitrogen. When the decarburization is completed, the carbon content inthe cold-rolled steel sheet may be 0.005 wt % or less. In one embodimentof the present invention, since the AlN grain growth inhibitor is notused, the nitriding process can be omitted.

Next, the cold-rolled sheet having undergone the primaryrecrystallization annealing is subject to a secondary recrystallizationannealing. At this time, after the annealing separator is applied to thecold-rolled sheet having undergone the primary recrystallizationannealing, secondary recrystallization annealing can be performed. Atthis time, the annealing separator is not particularly limited, and anannealing separator containing MgO as a main component can be used.

The step of secondary recrystallization annealing includes a temperatureelevating step and a cracking step. The temperature elevating step is astep of raising the temperature of the cold-rolled sheet, of which theprimary recrystallization annealing is completed, to the temperature ofthe cracking step. The temperature of the cracking step may be 900° C.to 1250° C. If the temperature is less than 900° C., the Goss grains maynot sufficiently grow and the magnetic properties may be deteriorated.When the temperature exceeds 1250° C., the grains may grow so large thatthe characteristics of the electrical steel sheet may be deteriorated.The temperature elevating step may be performed in a mixed gasatmosphere of hydrogen and nitrogen, and the cracking step may beperformed in a hydrogen atmosphere.

In the method of manufacturing a grain-oriented electrical steel sheetaccording to an embodiment of the present invention, since the AlN andMnS are not used as a grain growth inhibitor, the stress reliefannealing step can be omitted after the secondary recrystallizationannealing is completed.

In the conventional method of manufacturing a grain-oriented electricalsteel sheet using MnS and AlN as a grain growth inhibitor,high-temperature stress relief annealing to remove precipitates, such asAlN and MnS, is required. However, in the method of manufacturing agrain-oriented electrical steel sheet according to one embodiment of thepresent invention, the stress relief annealing process may not benecessary.

Thereafter, an insulating film may be formed on the surface of thegrain-oriented electrical steel sheet or a magnetic domain refiningtreatment may be carried out, if necessary. In one embodiment of thepresent invention, the alloy component of the grain-oriented electricalsteel sheet refers to a base steel sheet excluding a coating layer suchas an insulating film.

Hereinafter, the present invention will be described in more detail withreference to examples. However, the embodiments are only forillustrating the present invention, and the present invention is notlimited thereto.

EXAMPLE 1

A slab containing, by weight, Si: 3.2%, C: 0.05%, Mn: 0.06%, S: 0.0048%,N: 0.0032%, and Al: 0.005%, and barium (Ba), yttrium (Y), and boron (B)as shown in Table 1 below, and the remainder Fe and other inevitablyincorporated impurities, was prepared.

The slab was heated at a temperature of 1150° C. for 90 minutes, andhot-rolled to obtain a hot-rolled sheet having a thickness of 2.6 mm.The hot-rolled sheet was heated to a temperature of 1050° C. or higher,held at 910° C. for 90 seconds, cooled with water, and pickled. Andthen, the sheet was cold-rolled to a thickness of 0.30 mm through atotal of seven passes using a reverse mill. The reduction roll per passwas the same for each test condition. The cold-rolled steel sheet washeated in a furnace, and then held in a mixed gas atmosphere of 50 vol %of hydrogen and 50 vol % of nitrogen and annealing temperature of 850°C. for 120 seconds to carry out the primary recrystallization annealingalong with the decarburization was performed until carbon contentreaches 0.002 wt. %. Thereafter, MgO was applied and then wound into acoil, followed by the secondary recrystallization annealing. Thesecondary recrystallization annealing was carried out in a mixed gasatmosphere of 25 vol % of nitrogen and 75 vol % of hydrogen to elevatethe temperature to 1200° C. After reaching 1200° C., the sheet was heldin 100 vol % of hydrogen gas atmosphere for 20 hours, followed bycooling in the furnace.

After the surface of the final steel sheet was cleaned, the magneticflux density was measured at a magnetic field strength of 800 A/m usinga single sheet measurement method.

TABLE 1 magnetic Ba Y B ([Ba] + flux Sample Content Content Content[Y])/ density No. (wt %) (wt %) (wt %) ([B]*10) (B8, Tesla) Note 1 0.080 0.0015 5.3 rolling Comparative cracks material 2 0.08 0 0.003 2.7 1.91Inventive material 3 0.2 0 0.012 1.7 1.90 Inventive material 4 0.2 00.045 0.4 1.53 Comparative material 5 0 0.12 0.0033 3.6 rollingComparative cracks material 6 0 0.11 0.0035 3.1 rolling Comparativecracks material 7 0 0.25 0.043 0.6 1.90 Inventive material 8 0.08 0.020.024 0.4 1.55 Comparative material 9 0.13 0.05 0.005 3.6 rollingComparative cracks material 10 0.03 0.15 0.007 2.6 1.92 Inventivematerial 11 0.03 0.15 0 — rolling Comparative cracks material

As can be seen from Table 1, when the content of B was controlled withinthe range of the present invention depending on the contents of Ba andY, the inventive material had no rolling cracks and excellent magneticproperties were obtained compared to the comparative material.

In addition, in FIG. 1 and FIG. 2, the photograph of the cold-rolledsteel sheet in the manufacturing process of the inventive material ofthe Sample No. 2 and the photograph of the cold-rolled steel sheet inthe manufacturing process of the comparative material of the Sample No.1 were shown. It can be seen that the rolling cracks clearly appear inthe case of the comparative material.

EXAMPLE 2

A slab containing, by weight, Si: 3.2%, C: 0.048%, Mn: 0.11%, S:0.0051%, N: 0.0028%, and Al: 0.008%, and barium (Ba), yttrium (Y), andboron (B) as shown in Table 2 below, and the remainder Fe and otherinevitably incorporated impurities, was prepared.

The slab was heated at a temperature of 1150° C. for 90 minutes, andhot-rolled to obtain a hot-rolled sheet having a thickness of 2.6 mm.The hot-rolled sheet was heated to a temperature of 1050° C. or higher,held at 910° C. for 90 seconds, cooled with water, and pickled. Andthen, the sheet was cold-rolled to a thickness of 0.30 mm through atotal of seven passes using a reverse mill. The reduction roll per passwas the same for each test condition. The cold-rolled steel sheet washeated in a furnace, and then held in a mixed gas atmosphere of 50 vol %of hydrogen and 50 vol % of nitrogen and annealing temperature of 850°C. for 120 seconds to carry out the primary recrystallization annealingalong with the decarburization was performed until carbon contentreaches 0.003 wt. %. Thereafter, MgO was applied and then wound into acoil, followed by the secondary recrystallization annealing. Thesecondary recrystallization annealing was carried out in a mixed gasatmosphere of 25 vol % of nitrogen and 75 vol % of hydrogen to elevatethe temperature to 1200° C. After reaching 1200° C., the sheet was heldin 100 vol % of hydrogen gas atmosphere for 20 hours, followed bycooling in the furnace.

After the surface of the final steel sheet was cleaned, the magneticflux density was measured at a magnetic field strength of 800 A/m usinga single sheet measurement method. In addition, the particle diameter ofthe grains was calculated as the average value based on the area afterremoving the coating layer on the surface by immersing into ahydrochloric acid heated to 60° C. for 5 minutes.

TABLE 2 average particle of grains having 2 mm or more magnetic Ba Y B([Ba] + of particle flux Sample Content Content Content [Y])/ diameterdensity No. (wt %) (wt %) (wt %) ([B]*10) (mm) (B8, Tesla) Note 1 0.050.025 0.004 1.88 27 1.91 Inventive material 2 0.03 0.08 0.0032 3.44 —rolling Comparative cracks material 3 0.1 0.13 0.01 2.3 18 1.90Inventive material 4 0.04 0.043 0.01 0.83 22 1.90 Inventive material 50.15 0.08 0.0035 6.57 — rolling Comparative cracks material

Referring to Table 2, the average particle diameter of the grains having2 mm or more of particle diameter in the electrical steel sheetaccording to an embodiment of the present invention was found to be 10mm or more, and the magnetic properties were excellent.

It will be understood by those of ordinary skill in the art that variouschanges in form and details may be made herein without departing fromthe spirit and scope of the present invention as defined by thefollowing claims and their equivalents. It will be understood that theinvention may be practiced. It is therefore to be understood that theabove-described embodiments are illustrative in all aspects and notrestrictive.

DeletedTexts

What claimed is:
 1. A grain-oriented electrical steel sheet comprising,by weight, Si: 1.0 to 7.0%, B: 0.001 to 0.1%, and Ba and Y individuallyor in a total amount of 0.005 to 0.5%, and the remainder comprising Feand other unavoidable impurities.
 2. The grain-oriented electrical steelsheet according to claim 1, satisfying the following formula (1).0.5≤([Ba]+[Y])/([B]*10)≤3   [Formula 1] (In the Formula (1), [Ba], [Y],and [B] represent the contents (% by weight) of Ba, Y and B,respectively.)
 3. The grain-oriented electrical steel sheet according toclaim 1, further comprising C: 0.005% or less (excluding 0%), Al: 0.005%or less (excluding 0%), N: 0.0055% or less (excluding 0%), and S:0.0055% or less (excluding 0%).
 4. The grain-oriented electrical steelsheet according to claim 1, further comprising Mn: 0.01% to 0.5%.
 5. Thegrain-oriented electrical steel sheet according to claim 1, wherein theaverage particle diameter of the grains having a particle diameter of 2mm or more is 10 mm or more.
 6. The grain-oriented electrical steelsheet according to claim 1, comprising B and, Ba or Y segregated in thegrain boundaries.
 7. A method for manufacturing grain-orientedelectrical steel sheet comprising: a step of heating the slabcomprising, by weight, Si: 1.0 to 7.0%, B: 0.001 to 0.1%, and Ba and Yindividually or in a total amount of 0.005 to 0.5%, and the remaindercomprising Fe and other unavoidable impurities; a step of hot-rollingthe slab to produce a hot-rolled sheet; a step of cold-rolling thehot-rolled sheet to produce a cold-rolled sheet; a step of the primaryrecrystallization annealing the cold-rolled sheet; and a step of thesecond recrystallization annealing the cold-rolled sheet after theprimary recrystallization annealing is completed.
 8. The method formanufacturing grain-oriented electrical steel sheet according to claim7, wherein the slab satisfies the following Formula (1).0.5≤([Ba]+[Y])/([B]*10)≤3   [Formula 1] (In the formula (1), [Ba], [Y],and [B] represent the contents (% by weight) of Ba, Y, and B,respectively.)
 9. The method for manufacturing grain-oriented electricalsteel sheet according to claim 7, wherein the slab further comprises C:0.001 to 0.1%, Al: 0.01% or less (excluding 0%), N: 0.0055% or less(excluding 0%), and S: 0.0055% or less (excluding 0%).
 10. The methodfor manufacturing grain-oriented electrical steel sheet according toclaim 7, wherein the slab further comprises Mn: 0.01 to 0.5%.
 11. Themethod for manufacturing grain-oriented electrical steel sheet accordingto claim 7, wherein the slab is heated to 1000 to 1280° C. in the stepof heating the slab.
 12. The method for manufacturing grain-orientedelectrical steel sheet according to claim 7, wherein the final reductionroll is 80% or more in the step of cold-rolling the hot-rolled sheet toproduce a cold-rolled sheet.
 13. The method for manufacturinggrain-oriented electrical steel sheet according to claim 7, wherein thesecond recrystallization annealing step comprises a temperatureelevating step and a cracking step, and the temperature of the crackingstep is 900 to 1250° C.